Stabilization of the external kink and control of the resistive wall mode in tokamaks

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One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-n ideal MHD instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Experiments in the DIII-D, PBHX-M, and HBT-EP tokamaks have demonstrated that plasmas with a nearby conducting wall can remain stable to the n = 1 ideal external kink above the beta limit predicted with the wall at infinity, with durations in DIII-D up to 30 times {tau}{sub w}, the ... continued below

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18 p.

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Garofalo, A. M.; Turnbull, A. D. & Strait, E. J. January 1999.

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One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-n ideal MHD instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Experiments in the DIII-D, PBHX-M, and HBT-EP tokamaks have demonstrated that plasmas with a nearby conducting wall can remain stable to the n = 1 ideal external kink above the beta limit predicted with the wall at infinity, with durations in DIII-D up to 30 times {tau}{sub w}, the resistive wall time constant. More recently, detailed, reproducible observation of the n = 1 RWM has been possible in DIII-D plasmas above the no-wall beta limit. The DIII-D measurements confirm characteristics common to several RWM theories. The mode is destabilized as the plasma rotation at the q = 3 surface decreases below a critical frequency of 1 to 7 kHz. The measured mode growth times of 2 to 8 ms agree with measurements and numerical calculations of the dominant DIII-D vessel eigenmode time constants, {tau}{sub w}. From its onset, the RWM has little or no toroidal rotation and rapidly reduces the plasma rotation to zero. Both DIII-D and HBT-EP have adopted the smart shell concept as an initial approach to control of these slowly growing RWMs; external coils are controlled by a feedback loop designed to make the resistive wall appear perfectly conducting by maintaining a net zero radial field at the wall. Initial experiment results from DIII-D have yielded encouraging results.

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18 p.

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INIS; OSTI as DE99001451

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  • 40. annual physics of plasmas meeting, APS Division of Plasma Physics, New Orleans, LA (United States), 16-20 Nov 1998

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  • Other: DE99001451
  • Report No.: GA--A23023
  • Report No.: CONF-981127--
  • Grant Number: FG02-89ER53297;FG03-97ER54415;AC03-89ER51114;AC02-76CH03073;AC05-96OR22464;W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 304174
  • Archival Resource Key: ark:/67531/metadc686778

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  • January 1999

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  • July 25, 2015, 2:20 a.m.

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  • Aug. 23, 2016, 3:52 p.m.

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Garofalo, A. M.; Turnbull, A. D. & Strait, E. J. Stabilization of the external kink and control of the resistive wall mode in tokamaks, article, January 1999; San Diego, California. (digital.library.unt.edu/ark:/67531/metadc686778/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.